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We thank Eckles et al. (1) for their thoughtful comments. The authors point out that the optimization algorithms of Facebook’s advertising platform constitute a potential confound of campaign outcomes. We agree, in general, that such algorithms could pose a threat to the validity of field studies since they introduce unintended variance across the target audiences. However, as we demonstrate below, it is unlikely that such confounds account for the pattern of results presented in our original research (2).

First, the authors point toward “statistically significant” differences in the age and gender distributions of target groups. However, it is important to keep in mind that with sample sizes as …

Bacteria could help tackle the growing mountains of e-waste that plague the planet. Although researchers are a long way from optimizing the approach, some are already confident enough to pursue commercial ventures.

Holographic acoustic tweezers, in which ultrasonic waves produced by arrays of sound emitters are used to individually manipulate up to 25 millimeter-sized particles in three dimensions, could be used to create 3D displays consisting of levitating physical voxels.